The invention relates generally to electronic power conversion and more particularly to a solid state high voltage, fast rise/fall time, and variable pulse repetition rate pulse generator using inductive energy storage devices.
Voltage generators such as plasma generators capable of operating at high voltages with fast pulse rise and fall times, and high pulse repetition rates have generally employed radio frequency (RF) power amplifiers and related technology to accomplish high voltage, high speed and high pulse repetition rate generation and transmission. Such RF power amplifiers are expensive to produce and suffer in reliability due to internal heat build-up during high pulse repetition rate generation. RF amplifiers also undesirably require significant real estate and generally have low electric efficiency. Further, RF power amplifier technology is not particularly suitable for generation of high pulse repetition rates due to thermal losses, among other things.
Known high voltage pulse generators for the generation of plasma and the like generally employ gap type switches that substantially limit the upper pulse repetition rate as well as the overall system reliability level. These known high voltage pulse generation systems also require a substantial amount of real estate to provide a working system due to structural limitations.
Various voltage multiplication and transformation techniques were previously employed for the pulse power generators with an output voltage over tens of kV. The most famous Marx generator involves charging a bank of capacitors in parallel and discharging them in series by means of closing switches. The output voltage is effectively equal to N time of charging voltage, where N is the number of capacitors in series. The circuits of this type have found very wide application in pulsed power technology. The technical challenges lie in finding suitable closing switches and a fast, effective recharging circuitry for a fast rise time and high repetition rate.
The Fitch generator employs a similar concept to the Marx generator but with the number of switches being halved. Initially, the capacitor bank is charged from a dc voltage source, as in a Marx generator circuit. As the switches close, the even capacitors start discharging through the inductors L in an oscillatory fashion with a time period that equals π*sqrt(LC). The voltage across the capacitors reverses sign and the output voltage of the generator becomes N times the charging voltage, where N is the number of the stages. One added benefit of the Fitch generator is that the resistances and inductances of the switches have no effect on the circuit output impedance. However, the switches must be operated as simultaneously as possible and the LC stages must be constructed with identical time constants as much as possible.
Tesla transformers, line transformers, conventional pulse transformers and autotransformers are magnetically coupled devices and widely used to multiply input voltage. However, because of their poor frequency characteristics, they cannot be employed directly in nanosecond pulse power technology, but generally on the microsecond time scale.
Other techniques, such as voltage adders consisting of N single-turn pulse transformers with a common secondary winding, have demonstrated usefulness in voltage multiplication. However, the choice of the close switch type, recharging circuit and physical construction pose significant challenges. One significant challenge is associated with the electromagnetic compatibility (EMC) design concepts. Due to the tremendous amount of high power generated within nanosecond time scales and repetitive requirements at tens of kilo hertz, the emitted electromagnetic energy by the plasma may cause an improper operation of the pulse generator and other equipment as well in the same electromagnetic environment. Susceptibility and/or immunity design features of the pulse power generator are therefore very important when used in practical applications.
It would be both advantageous and beneficial to provide a high voltage, fast rise/fall time, high pulse repetition rate pulse generator with electromagnetic hardening enhancement features that overcome the high pulse repetition rate limitations associated with conventional high voltage pulse generators. It would be further advantageous if the high voltage, fast rise/fall time, high pulse repetition rate pulse generator were capable of continued operation without impairment of the pulse generator during substantially longer time periods than that achievable using conventional high voltage pulse generators. It would be further advantageous if the high voltage, fast rise/fall time, high pulse repetition rate pulse generator occupied substantially less real estate to provide a working system than that required by conventional high voltage pulse generators.